tier

tier is a Rust configuration library for typed, layered application config.

It is built for projects that want one serde config type fed by code defaults, TOML files, environment variables, and CLI overrides.

By default, tier only enables TOML support. derive, clap, schema, watch, json, and yaml stay opt-in.

What It Does

• Loads config from defaults, files, env, and CLI in a predictable order
• Deserializes directly into typed Rust structs
• Treats env and --set inputs as strings first, with primitive coercion at deserialize time
• Tracks where each value came from and surfaces validation and warning output
• Optionally adds derive metadata, schema/docs export, and runtime reload

Quick Start

use serde::{Deserialize, Serialize};
use tier::ConfigLoader;

#[derive(Debug, Clone, Serialize, Deserialize)]
struct AppConfig {
    port: u16,
}

impl Default for AppConfig {
    fn default() -> Self {
        Self { port: 3000 }
    }
}

let loaded = ConfigLoader::new(AppConfig::default())
    .file("config/app.toml")
    .load()?;

assert_eq!(loaded.config().port, 3000);
# Ok::<(), tier::ConfigError>(())

Feature Flags

• toml: TOML file parsing and commented TOML examples
• derive: #[derive(TierConfig)] metadata generation
• clap: reusable config flags and diagnostics commands
• schema: JSON Schema, env docs, and machine-readable reports
• watch: native filesystem watcher backend
• json: JSON file parsing
• yaml: YAML file parsing

Examples And Docs

• Crate documentation: crates/tier/README.md
• Examples: crates/tier/examples
• API docs: https://docs.rs/tier

Scope

Current scope stays focused on typed layered loading, metadata, diagnostics, validation, schema/docs output, and reload support.

Out of scope for the current crate line:

• remote configuration backends
• full application-specific CLI generation from derive metadata